also when I purchased our f250 w/6.0 I checked with the service manager about using biodiesel in it and he said to go ahead as long as it meets the fuel specs in the owners manual. which if you check the biodiesel.org site it does. and my local fuel supplier confirmed it.
Michigan State University is also using biodiesel in all of it's diesels on campus. Plus several schools in Michigan are using it in buses.